Method of producing metal-containing particles

ABSTRACT

A method of producing metal-containing particles. The metal-containing particles are micro-sized and/or nano-sized particles. The particles may have anti-microbial properties depending on the metal used. For embodiments wherein silver is used, the particles may also provide and-fungal properties, anti-static properties, electromagnetic interference shielding, and/or conductive properties. The particles may range in size from about 0.01 to about 300 μm.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of U.S. provisional patent application No. 60/501, 084, filed Sep. 9, 2003.

FIELD OF THE INVENTION

This invention is directed generally to particles, and more particularly to methods of making micro-particles and/or nano-particles

BACKGROUND OF THE INVENTION

There has been a great deal of attention in recent years given to the hazards of bacterial contamination from potential everyday exposure. With such an increased consumer interest in this area, manufacturers have begun introducing antimicrobial agents within various household products and articles. For instance, certain brands of polypropylene cutting boards, liquid soaps, etc., all contain antimicrobial compounds.

In addition, the risk of bacterial infection is also prevalent in medical instances. For example, a variety of medical articles are designed particularly for contact with a patient's bodily fluids. The duration of this contact may be relatively short, as is typical with wound dressings, or may be long tern as is typical with prosthetic heart valves implanted into the body of a recipient. Some articles such as catheters may have either short term or relatively long term contact. Other articles typically having relatively short term contact with the patient include, without limitation, burn dressings and contact lenses. Other articles typically having long term contact with a patient include, without limitation, implanted prostheses.

Contact of articles with bodily fluids creates a risk of infection This risk may be very serious and even life threatening. In addition, considerable costs, and longer or additional hospital stays may result due to infection. For example, infections associated with dressings may increase the seriousness of the injury for burn victims. Also, infection associated with an implanted prosthesis may necessitate replacement of the device.

Accordingly, the prior art has attempted to examine methods to help reduce the risk of bacterial infection and/or to prevent infection from even occurring. One approach has been through the use of anti-microbial agents and/or microbiocides.

The most popular antimicrobial for many articles is triclosan. Although the incorporation of such a compound within liquid or polymeric media has been relatively simple, other substrates, including the surfaces of textiles and fibers, have proven less accessible. There has a long-felt need to provide effective, durable, and long-lasting antimicrobial characteristics for textile surfaces, in particular on apparel fabrics, and on film surfaces. Such proposed applications have been extremely difficult to accomplish with triclosan, particularly when wash durability is a necessity (triclosan easily washes off any such surfaces). Furthermore, although triclosan has proven effective as an antimicrobial compound, the presence of chlorines within such a compound causes skin irritation which makers the utilization of such with fibers, films, and textile fabrics for apparel uses highly undesirable.

Furthermore, there are commercially available textile products comprising acrylic and/or acetate fibers co-extruded with triclosan (for example Celanese markets such acetate fabrics under the name Microsafe™ and Acordis markets such acrylic fibers, under the tradename Amicor™). However, such an application is limited to those types of fibers; it does not work at all for natural fibers and specifically does not work for and/or: within polyester, polyamide, cotton, spandex, etc., fabrics. Furthermore, this co-extrusion procedure is very expensive. In addition, the zone of inhibition for the anti-microbial agent is limited in these applications.

Silver-containing inorganic microbiocides have recently been developed and utilized as antimicrobial agents on and within a plethora of different substrates and surfaces. In particular, such microbiocides have been adapted for incorporation within melt spun synthetic fibers, as taught within Japanese unexamined Patent Application No. H11-124729, to provide certain fabrics which selectively and inherently exhibit antimicrobial characteristics. Furthermore, attempts have been made to apply such specific microbiocides on the surfaces of fabrics and yarns with little success from a durability standpoint. A topical treatment with such compounds has never been successfully applied as a durable finish or coating on a fabric or yarn substrate.

There have been improvements in the area of fiber technology that permit the formation of silver textiles in an efficient and/or cost-effective manner. However, these manners are still directed to the formation of fibers and fabrics having silver thereon. In some instances, these fabrics and fibers are not useful as the size of the fabric or fiber is too big for the selected application.

Accordingly, what is needed is a method of preparing metal-based particles that have greater utility than prior art anti-microbial solutions. Also what is needed is a method for producing micro-sized and/or nano-sized particles containing silver.

SUMMARY OF THE INVENTION

The present invention provides a method of producing metal-containing particles. The metal-containing particles are micro-sized and/or nano-sized particles. The metal is complexed with an alkali agent to form the particles. In one embodiment, the metal is silver and the particles include silver hydroxide. The particles have anti-microbial properties. For embodiments wherein silver is used, the particles may also provide anti-fungal properties, and-static properties, and/or conductive properties. The particles may range in size from about 0.01 to about 300 μm.

These and other embodiments are described in more detail below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the following description and examples that are intended to be illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, the singular form “a,” “an,” and “the” may include plural referents unless the context clearly dictates otherwise. Also, as used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.”

The present invention provides a method of preparing metal-based particles. In one aspect, the method is used to form micro-sized and/or nano-sized particles that include a metal. In one embodiments the metal is silver. These micro-sized and/or nano-sized particles have utility in a wide variety of different applications due to their size. Additionally, these particles retain the anti-microbial, anti-fungal, anti-static, and/or conductive properties of the metal used. As a result, microsized and/or nano-sized particles including silver offer one or more properties such as anti-microbial, anti-static and/or conductive.

Accordingly, in one aspect, the present invention provides a method of making micro-sized and/or nano-sized metal-containing particles. In one embodiment, the metal is silver. In alternative embodiments, the metal may be copper, aluminum, zinc, nickel, or the like. The method makes micro-sized and/or nano-sized particles that contain a metal, such as silver. As used herein, “micro-sized particles” are particles that have a diameter of from about 1 to about 300 μm. As used herein, “nano-sized particles” are particles that have a diameter of from about 0.01 to about 1 μm. Depending on different process parameters, the method may be used to form micro-size particles only, nano-sized particles only, or a combination thereof, with the resulting mixture either being used as a mixture, or further including a separation step to sort the particles into different size ranges. One example of such a separation step is a screening step to separate the particles into different sizes.

The methods of the present invention form these metal-containing particles using a series of process steps, although not all process steps are necessary for each embodiment. The first step is to take a source of the metal, such as silver nitrate powder for embodiments wherein silver particles are to be formed, and dissolve it in water. In one embodiment, the water is de-ionized water. In an alternative embodiment, a pre-dissolved silver nitrate solution may be used provided the amount of water in the solution is known. The table below references to different embodiments for various amounts of silver nitrate and water that may be used in an embodiment wherein the source of silver is silver nitrate and de-ionized water is used. Amount of Silver Nitrate in gm per liter of DI water First Embodiment about 3 to about 500 Second Embodiment about 50 to about 350 Third Embodiment about 100 to about 200 Fourth Embodiment about 150

The above mentioned solution may then treated with an alkali solution. In one embodiment, the alkali solution is sodium hydroxide. Sodium hydroxide may be used due to its great tendency to complex with the metallic solution. However, any alkali solution that is able to complex with the metallic solution used in a particular embodiment may be used in the present invention. In this embodiment, the metallic solution is silver nitrate dissolved in DI water. Other alkali solutions that may be used include, but are not limited to, ammonium hydroxide.

The table below references to different embodiments of the present invention for various amounts of sodium hydroxide that may be used in those embodiments wherein sodium hydroxide is the alkali solution. It should be noted that the starting point to make the solution is 50% sodium hydroxide solution (50:50 v/v) which is readily available form multiple vendors. ml of NaOH from 50:50 First Embodiment about 10 to about 500 Second Embodiment about 50 to about 300 Third Embodiment about 75 to about 150 Fourth Embodiment about 100

The reaction may take place at room temperature, or at a temperature of from about 15 to about 30° C. During the reaction, the alkali solution complexes with the metal to form a precipitate containing the metal. In those embodiments wherein sodium hydroxide is used, brown precipitate is formed as the sodium hydroxide is added. The solution may be stirred while the precipitate is forming. After all the alkali solution is added, the resultant mixture may be allowed to settle down for a period of time to permit settling of any precipitate. The amount of time permitted for setting may vary, but may be from about 5 to about 15 minutes.

After settling, the precipitate is then removed. The precipitate may be filtered using standard filter paper, such as a Buckner funnel. Depending on the pH of the solution, the solution may be neutralized. As the alkali solution will generally increase the pH to above 7, an acid may be used to bring the solution to a pH of approximately 7. In one embodiment, sulfuric acid may be used, although other acids may also be used including, but not limited to, hydrochloric acid and nitric acid, among others. Bringing the pH of the solution to about 7 is beneficial in that it will facilitate easy processing from waste treatment point of view, although this step is not necessary in the formation of the micro-sized and nano-sized particles of the present invention.

The precipitate is then rinsed with water, such as deionized water. The water is, beneficially, used to wash the precipitate thoroughly. Washing of the precipitate helps facilitate nano- and micro-sized particles of the complexed metal precipitate to be collected in pure form. In an embodiment wherein silver is the metal and sodium hydroxide is the alkali solution, the resulting precipitate includes nano- and micro-sized particles of silver hydroxide. The rinsing may be done anywhere, including within the funnel itself.

The precipitate may then be dried in a conventional oven or other drying mechanism until the precipitate is substantially dry. In one embodiment, the drying temperature is from about 50 to about 90° C. After drying the precipitate, the resulting product includes the micro-sized and/or nano-sized particles of the present invention.

It is to be understood that since the micro-sized and/or nano-sized particles of the present invention include silver, the beneficial properties of silver are retained, even with the smaller size of the particles. As a result, the particles of the present invention may be used in any application taking advantage of one or more of the beneficial properties of silver. These properties include, but are not limited to, anti-microbial, anti-fungal, anti-static, conductive, electromagnetic interference (EMI) shielding, filtration, or a combination thereof.

The present invention will now be further described through examples. It is to be understood that these examples are non-limiting and are presented to provide a better understanding of various embodiments of the present invention.

EXAMPLES Example 1

75 gm of silver nitrate salt was weighed out This was then dissolved in 500 ml of deionized water at room temperature (app. 22° C.). Upon dissolving the salt the final volume could raise up to 600 ml. 100 ml of 50:50 NaOH was added slowly to the silver nitrate solution. A brown precipitate formed immediately. The solution with precipitate was then stirred with a rod. The mixture was then allowed to settle down for about 10 minutes. The precipitate was then filtered using standard filter paper using a buckner funnel.

The solution was neutralized using 50% sulfuric acid The precipitate was then rinsed with deionized water using 50-100 ml at a time through the buckner funnel. 5000 ml of DI water was used to rinse the precipitate in this example

The resulting precipitate was then dried in a conventional oven until dry at temperature maintained between about 60 to about 80° C.

Approximately 46 gm of brown silver hydroxide nano- and micro-sized particulates were collected.

Example 2

The resultant nano powder obtained from Example 1 was then subjected to high heat (i.e. greater than about >100° C.) for a few minutes. This heating resulted in the formation of shiny white micro- and nano-sized particles of silver. The resultant powder weighed approximately 43 gm.

Example 3

The resultant powder from Example 1 was then incorporated into the outer surface of a hydrogel bandage at the ratio of 10:1 by weight of the hydrogel to the weight of the silver powder. The surface was dipped to apply the hydrogel mixture to the surface. This sample was then subjected to Dow Corning Corporate Test Method 0923 using Staphylococcus aureus ATCC 6538. After 1 hour the organism count CFU/ml reduced from 1.6×10⁵ at zero time to <10. The percentage reduction was >99.99%. As a result, the anti-microbial properties of the micro- and nano-sized silver hydroxide particles is clearly seen.

Example 4

The resultant powder from Example 1 was then incorporated into the outer surface of a hydrogel bandage at the ratio of 10:1 by weight of the hydrogel to the weight of the silver powder and then subjected to the same test as Example 3 over a period of 4 hours. The reduction was again 99.99%. This clearly suggests the enormous surface area of the nano particles and its effectiveness in small quantities.

Example 5

The resultant powder from Example 1 was then incorporated into the outer surface of a hydrogel bandage at the ratio of 100:1 by weight of the hydrogel to the weight of the silver powder and then subjected to the same test as Example 3 over a period of 4 hours. The reduction was an amazing 94%, again indicating the effectiveness of the nano particles as well as the surface area benefits. The test result also indicates a great zone of inhibition of the nano particles.

The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention. 

1. A method of making metal-containing particles comprising: forming a solution of a metal in a solvent; mixing the metal solution with an alkali solution to form a precipitate containing the metal; separating the precipitate; and drying the precipitate to form the metal-containing particles.
 2. The method of claim 1, wherein the metal is selected from silver, copper, nickel, zinc, aluminum, or a combination thereof.
 3. The method of claim 2, wherein the metal is silver.
 4. The method of claim 1, wherein metal-containing particles range in size from about 0.01 μm to about 300 μm.
 5. The method of claim 4, wherein metal containing particles range in size from about 1 μm to about 300 μm.
 6. The method of claim 4, wherein metal-containing particles range in size from about 0.01 μm to about 1 μm.
 7. The method of claim 1, further comprising the step of rinsing the precipitate with water prior to drying.
 8. The method of claim 1, wherein the solution of a metal in a solvent comprises silver nitrate powder dissolved it in water.
 9. The method of claim 8, wherein the amount of silver nitrate in grams per liter of water is from about 3 to about
 500. 10. The method of claim 9, wherein the amount of silver nitrate in grams per liter of water is from about 100 to about
 200. 11. The method of claim 1, wherein the alkali solution is selected from sodium hydroxide, ammonium hydroxide, or a combination thereof.
 12. The method of claim 11, wherein the alkali solution is sodium hydroxide.
 13. The method of claim 12, wherein the sodium hydroxide solution is a 50% (v/v) sodium hydroxide solution.
 14. A particle made by the method of claim
 1. 15. The particle of claim 1, wherein the metal is selected from silver, copper, nickel, zinc, aluminum, or a combination thereof.
 16. The particle of claim 15, wherein the metal is silver.
 17. The particle of claim 14, wherein metal-containing particles range in size from about 0.01 μm to about 300 μm.
 18. The particle of claim 17, wherein metal-containing particles range in size from about 1 μm to about 300 μm.
 19. The particle of claim 17, wherein metal-containing particles range in size from about 0.01 μm to about 1 μm.
 20. A silver hydroxide particle comprising: silver complexed with a hydroxide; wherein the particle is from about 0.01 μm to about 300 μm in diameter. 